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Biomedical subjects

A Rosenfalck

Publications and source records attributed to A Rosenfalck.

At least 19 recordsLinked to original sources
PubMed1998

Long-term administration of theophylline and glucose recovery after hypoglycaemia in patients with type 1 diabetes mellitus.

The methylxanthine theophylline increases intrahepatic c-AMP and c-AMP mediates the hepatic glucose response to adrenaline and glucagon. Intravenous theophylline increases glucose recovery during acute insulin-induced hypoglycaemia and caffeine increases hypoglycaemia awareness and glucoregulatory hormone secretion. In this study we tested the hypothesis that long-term administration of theophylline might augment glucose recovery after insulin-induced hypoglycaemia. Eleven healthy subjects and 8 patients with Type 1 diabetes mellitus were made hypoglycaemic by 60 min insulin infusion (40 mU m(-2)) after 2 weeks' oral therapy with Euphyllin Retard (theophylline) or placebo. Plasma glucose nadir was 2.54 (2.31-2.77) mmol l(-1) after Euphyllin Retard and 2.27 (2.05-2.48) mmol l(-1) after placebo (mean difference 0.26 (0.05-0.58) mmol l(-1), p = 0.09) for healthy control subjects and 2.56 (2.07-3.04) mmol l(-1) and 2.19 (1.37-2.65) mmol l(-1) (mean difference 0.38 (0.12-0.63) mmol l(-1), p = 0.01), respectively, for diabetic patients. The area under the glucose curve was greater after theophylline treatment for healthy control subjects (p = 0.0292) and for diabetic patients (p = 0.0241) but there were no concomitant significant increases in plasma c-AMP or in endogenous glucose production rate. Whether the increase in glucose recovery is large enough to suggest that chronic theophylline administration will protect against insulin-induced hypoglycaemia remains unsettled.

Adult↗
PubMed1996

Discrimination between artefacts and contractions in pressure signals from the gastrointestinal tract by pattern recognition method.

A pattern recognition algorithm has been developed to discriminate between artefacts and contractions in interdigestive motility recorded by a pressure catheter with four channels from the human duodenum. A learning and a test set, both containing natural and induced artefacts, such as respiration and body movement, are obtained from five volunteers. The event classes were phase I, II and III contractions of the interdigestive motility complex and artefacts from respiration, cough, calibration signals and movements. Length, area, amplitude, inter-event interval, up- and downstroke, and correlation to other pressure channels and to respiration, are applied to classify the events. The sensitivity of the computer scoring increases with the number of applied features. When all the features are applied, the sensitivity of the Bayes' classifier against the visually scored contractions and artefacts is 0.96 with a specificity of 0.69.

Adult↗
PubMed1996

Modelling techniques and their application for monitoring in high dependency environments--learning models.

This paper reviews the use of learning models including Bayesian classifiers and artificial neural networks in monitoring and interpreting biosignals. Generally learning models applied for analysis of biosignals are "black-box' types trained on the basis of measured signals. It is illustrated that the training and application of learning models more or less follow the same sequences. The main focus is the interpretation of electrical signals from the brain (electroencephalogram (EEG) and evoked potentials (EP)). Current analysis of these signals often reveals sudden changes in the EEG or evoked potentials to be the earliest discernible signs of inadequate perfusion of the brain. They may reflect problems such as systemic arterial oxygen desaturation or hypotension arising from other body system failures during critical illness. It is suggested that these brain signals should be recorded in the critical care unit, and that they should form part of the annotated database of biosignals established during the IMPROVE project. This would allow for the development of new methods for on-line warning of impending damage to the central nervous system, such that corrective actions could be taken before permanent damage occurred.

Auscultation↗
PubMed1996

Evaluation of the diagnostic performance of the expert EMG assistant MUNIN.

The diagnostic performance of the medical expert system MUNIN for diagnosis of neuromuscular disorders was evaluated on a set of 30 test cases. The cases were provided by 7 experienced electromyographers who were subsequently invited to participate in the evaluation. To reasonably cover the range of disorders, the electromyographers were asked to provide cases from patients with different types of muscular dystrophy, with neuromuscular transmission disorders, with motor neurone disease, and with different types of polyneuropathies. In addition, patients with a range of local neuropathies were provided. Out of the 30 cases, 11 cases were evaluated by an "almost peer review" method and the remaining 19 cases were evaluated by a "silver standard" method. The number of cases evaluated by "almost peer review" was limited to 11 due to time constraints on the evaluation procedure. During the "almost peer review," each electromyographer was asked to diagnose patients, using a vocabulary that closely resembled MUNIN's vocabulary. Subsequently, we attempted to provide a consensus diagnosis for the patients based on discussion among the participating electromyographers. The electromyographers were also asked to assess how well MUNIN had performed in each case. The remaining 19 cases were evaluated by a "silver standard" procedure, where MUNIN's diagnosis was compared to the diagnosis of the expert who provided the case. The results indicated that MUNIN performed well, and the electromyographers considered "that MUNIN performed at the same level as an experienced neurophysiologist." In particular, it was noted that MUNIN handled cases with conflicting findings well, and that it was able to diagnose patients with multiple diseases.

Diagnostic Services↗
PubMed1994

Detection of EEG patterns related to nocturnal hypoglycemia.

The aim of the project was to detect specific EEG patterns related to hypoglycemia. EEG analysis was performed using a probabilistic classifier and unsupervised learning for the construction of learning sets for the classifier. Unsupervised learning and additional tools were used in the search for EEG patterns occurring when the blood-glucose level was below the hypoglycemic threshold. The rate of these specific EEG patterns was below 5% in normal nights. In patients who were known to have no or a reduced glucagon response to hypoglycemia, the rate increased to 20-80%.

Adult↗
PubMed1992

Simultaneous electromyography and 31P nuclear magnetic resonance spectroscopy--with application to muscle fatigue.

The electromyogram (EMG) is often used to study human muscle fatigue, but the changes in the electromyographic signals during muscle contraction are not well understood in relation to muscle metabolism. The 31P NMR spectroscopy is a semi-quantitative non-invasive method for studying the metabolic changes in human muscle. The aim of this study was to develop a method by which EMG and NMR spectroscopy measurements could be performed simultaneously. All measurements were performed in a whole body 1.5 Tesla NMR scanner. A calf muscle ergometer, designed for use in a whole body NMR scanner, was used. The subject had the left foot strapped to the ergometer. The anterior tibial EMG was recorded by bipolar surface electrodes. A surface coil was strapped to the anterior tibial muscle next to the EMG electrodes. Simultaneous measurements of surface EMG and surface coil 31P NMR spectroscopy were performed in the scanner during an isometric submaximal voluntary contraction until exhaustion, in 6 normal volunteers. Concentrations of phosphocreatine (PCr), inorganic phosphate (P(i)) and pH were analysed together with root mean square (RMS) and median frequency of the EMG. The fatiguing contractions (endured 5-13 min) produced a rapid decline in PCr and pH accompanied by a rapid rise in P(i). The RMS was approximately constant until the normalized PCr concentration declined below 0.6-0.7 and the pH declined below 6.75-6.85; exceeding these metabolic limits was associated with a rapidly increasing RMS value (2-3 times the previous level by exhaustion). The median frequency declined linearly with time and was found to be highly linearly correlated with the pH value (r = 0.82).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Sleep disturbances in IDDM patients with nocturnal hypoglycemia.

Eight insulin-dependent diabetic patients were studied to evaluate sleep patterns during normoglycemia and spontaneous and insulin-induced hypoglycemia. Two channels of electroencephalogram (EEG), electromyogram and actooculogram were recorded. The signals were analyzed off-line, using a polygraphic sleep analysis system. The scoring was mainly based on the color density spectral array of the EEG. Blood glucose and growth hormone were measured serially. Asymptomatic, spontaneous nocturnal hypoglycemia occurred in 38% of the nights. Conventional sleep analysis showed a tendency toward prolongation of the two first rapid eye movement cycles on hypoglycemic nights, although it was insufficient to explain the activities seen during hypoglycemia. Blood glucose values below 2.0 mmol/l were observed in some of the patients accompanied by EEG changes with increased theta and delta activity.

Adult↗
PubMed1989

Computerized monitoring of depth of anaesthesia with isoflurane.

Changes in brain activity were studied at different depths of isoflurane anaesthesia. Ten healthy women (ASA group I) were investigated during non-critical surgery. Two channels of the EEG were stored on tape simultaneously with alveolar concentration of carbon dioxide, inspired oxygen concentration, mean arterial pressure, ECG and temperature. Signal processing was made offline. Spectral information from 2-s EEG segments was extracted using autoregressive modelling. Repetitive hierarchical clustering was used to define a common learning set of basic patterns. With this learning set, the EEG was classified, and the results presented in a class probability histogram. The basic patterns were related to the clinical depth of anaesthesia in all patients and assigned specific colours. Using this colour code, the class probability histogram showed a high degree of simplicity. Decreasing or increasing the isoflurane concentration caused the same trend in the class profile in all patients. This indicates that the EEG pattern might be a sensitive tool for decision making during administration of general anaesthetics.

Adult↗
PubMed1989

Consistency in manual scoring analysis of gastrointestinal pressure recordings.

The aim of the present study was to evaluate the consistency in visual scoring and whether this could be the basis for computer analysis using pattern recognition techniques. We studied the consistency of visual scoring of pressure tracings from the upper gastrointestinal tract with regard to pressure wave identification. The aim was to make such an identification the golden standard for computerized analysis of pressure waves. Pressure recordings containing different phases of contraction activity were evaluated by five trained observers. The inter- and intra-observer agreement was highest in periods with high contraction activity (phase III), both of which were better than 90%. In periods with low contraction activity (phases I and II) this agreement was as low as 49%. The results indicate that forming a learning set for pattern recognition should only be based on visual scoring during phase-III activity.

Adult↗
PubMed1986

Quantitative analysis of individual motor unit potentials: a proposition for standardized terminology and criteria for measurement.

The physiology of the motor unit potential (MUP) is reviewed. The aim is to identify the electrophysiological events in the motor unit that generate the individual parts of the MUP. This is based on insight gained from new experimental techniques, such as single-fiber electromyography (EMG), scanning EMG, and simulation studies of the MUP. A terminology for the different parts of the MUP is also suggested, and nine parameters used to describe different features of the MUP are delineated: duration, spike duration, amplitude, area, spike area, phases, turns, satellites, and variability. Technical aspects, such as electrode type, filtering, and sampling rate of the computers, are discussed as well. In Appendix A, different manual and computer-aided methods for quantitative MUP analysis are described. Despite minor systematic differences between the methods, MUP durations measured by different methods correlate highly with each other (Appendix B). The manual and computer-aided methods have comparable variability between repeated measurements.

Action Potentials↗
PubMed1980

Regulation of the firing pattern of single motor units.

The normal control of force in the anterior tibial muscle was reflected by a fast regulation of the interval pattern of single motor units. Short and long intervals alternated, the correlation between successive intervals was negative and "double discharges" were present. The discharge rate at 60% of maximal effort was at most 20 Hz.

Adolescent↗
PubMed1980

Impaired regulation of force and firing pattern of single motor units in patients with spasticity.

Patients with spasticity were unable to maintain a constant force of the anterior tibial muscle. The force at maximal effort was reduced to less than 40% of normal, partly because motor units fired at a reduced rate even at high levels of contraction. Force and instantaneous frequency fluctuated slowly. The fast regulation of the firing rate, which characterises normal muscle, was absent. The variation between successive intervals was less than normal and the serial correlation coefficient between intervals increased.

Adult↗
PubMed1974

Electrophysiological findings in entrapment of the median nerve at wrist and elbow.

In 117 consecutive patients with carpal tunnel syndrome and 11 patients with a compression syndrome of the median nerve at elbow, motor and sensory conduction along the median and ulnar nerves and quantitative electromyography were compared with findings in 190 normal controls of the same age. In 25% of patients with carpal tunnel syndrome in whom motor conduction and EMG were normal, the lesion was located from abnormalities in sensory conduction. The fact that conduction along the same fibres was moderately slowed from digit to palm, severely slowed across the flexor retinaculum, and normal from wrist to elbow indicates that slowing was due to demyelination at the site of compression. Fifteen per cent of the patients with carpal tunnel syndrome had clinical and electrophysiological signs of ulnar involvement. In the other patients conduction along the ulnar nerve was as in 100 normal controls. Compression at the elbow was located by electromyographical findings rather than by abnormalities in conduction.

Action Potentials↗
PubMed1971

Sensory conduction from digit to palm and from palm to wrist in the carpal tunnel syndrome.

In normal subjects the maximum and minimum conduction velocity along sensory nerve was the same from digit to palm and from palm to wrist. Severe slowing from palm to wrist in patients with the carpal tunnel syndrome was often associated with only slight slowing from digit to palm. The distal slowing is attributed to a reversible constriction of nerve fibres, an assumption supported by the recovery in distal conduction velocity as early as two and a half months after decompression. The sensory velocity from wrist to elbow was normal or supernormal, whereas the motor velocity was often slightly decreased. The exclusion of the normal segment of the median nerve distal to the flexor retinaculum made it possible to demonstrate abnormalities across the flexor retinaculum in patients with clinical signs of carpal tunnel syndrome in whom distal motor latency and sensory conduction from digit to wrist were normal.

Adult↗